Sulfonyl chlorides are widely used in the chemical industry such as for the preparation of dyes, lithographic resists, and pharmaceuticals. They can be further transformed into other functional groups such as aromatic sulfones (by Friedel-Crafts sulfonylation of aromatic substrates) or sulfonamides (by reaction with amines) (see, e.g., Kirk-Othmer Encyclopedia of Chemical Technology). Sulfonamides are integral functional groups of a wide variety of therapeutic small molecule drugs such as antibacterial agents, diuretics, and cPLA2 inhibitors.
A typical preparation of sulfonyl chlorides involves reaction of the sodium salt of a sulfonic acid with phosphorus pentachloride, sometimes in combination with phosphorus oxychloride or thionyl chloride, frequently with heating of the reaction mixture (see, e.g., March, Advanced Organic Chemistry, 4th ed., John Wiley & Sons, 1992, p. 499). These relatively harsh reaction conditions are unsuitable for the preparation of sterically hindered sulfonyl chlorides, such as arylalkylsulfonyl chlorides and the like, which can result in low yields due to the elimination of sulfur dioxide (Nakayama et al., Tet Lett., 1984, 25, 4553-4556). A milder, infrequently used method for the synthesis of sulfonyl chlorides is the reaction of tetrabutylammonium salts of sulfonic acids with triphenylphosphine/sulfuryl chloride (Widlanski et al., Tet Lett., 1992, 33, 2657-2660), a method that suffers from the disadvantage of poor atom efficiency.
Numerous sterically hindered sulfonyl halides such as (2,6-dimethylphenyl)-methanesulfonyl chloride and other aryl- and heteroaryl-sulfonyl halides are specifically useful in the preparation of cPLA2 inhibitors for the treatment of asthma or arthritic and rheumatic disorders as described in, for example, WO 2003/048122. As discussed above, these intermediates can be difficult to prepare due to loss of sulfur dioxide at higher temperatures and formation of significant amounts of impurities. Thus, new and improved methods for making these compounds are needed, and the methods provided herein help meet these and other needs.